Project Summary The goal of our research is to understand the mechanism of HIV-1 Tat-induced transcription at the HIV-1 promoter in T cells. Tat regulates the transition from mRNA initiation to elongation through direct interaction with the host cell P-TEFb RNAPII CTD kinase. During the previous period of funding, we identified SKIP as a P-TEFb-associated elongation factor that functions downstream of the Tat:P-TEFb to recruit c-Myc and TRRAP to the viral genome and promote H3K4 methylation at the integrated HIV-1 proviral promoter. We find that both SKIP, c-Myc and Tat:P-TEFb interact with MLL1:Menin, one of several mammalian H3K4 methyltransferase enzymes, to regulate HIV-1 H3K4 levels. Stable binding of SKIP to chromatin requires H2B ubiquitination, which is known to be essential for H3K79 methylation by the Dot1:AF4 complex, implicating SKIP in H3K79 methylation. This latter link is especially intriguing given the AF4 interacts directly with P-TEFb and is required for its CTD kinase and transcription activities in vivo. Here we will examine the role of these factors in establishing elongation and H3K4 and H3K79 methylation upon induction by Tat:P-TEFb, and also carry out biochemical studies to identify new components of the native SKIP transcription elongation complex, which may also be essential for Tat transactivation. Importantly, SKIP is known to also repress its target genes in the absence of induction, through binding to the CBF-1 enhancer factor, whicih was recently shown to be critical for repression of HIV-1 in latently-infected CD4(+) T cells. Therefore, we will also assess the role of SKIP and associated corepressors in the silencing of viral transcription in J-Lat cells, a model of HIV-1 latency.